The present invention relates to a device for temperature responsive switching of overflow fuel quantities from a diesel fuel injection pump to a fuel supply tank or to a filter in a fuel supply system of a diesel engine.
A temperature responsive switching device of the type under discussion has been disclosed, for example in U.S. Pat. No. 3,768,454. In the disclosed switching device a longitudinally movable piston slide is arranged in a longitudinal bore of the housing for switching the direction of diesel fuel. The piston slide is actuated by a thermostat against the action of a spring. The device with the longitudinal slide and the thermostat is rather expensive and requires a great deal of space. A further disadvantage of the known switching device resides in that the thermostat accummulates contamination particles and has a relatively great hysteresis. It is especially difficult to adjust the device during the winter time as well as during the summer time. Still another disadvantage of the known device is that the thermostat is always positioned in the main flow of the diesel fuel and therefore is exposed to the diesel fuel flowing from the tank or the mixed fuel flow and to the overflow fuel quantities from the fuel injection pump. This arrangement increases wear and hysteresis in the device first of all because no continuous air venting is possible at the start cold phase of operation, particularly in a small circuit of the overflow fuel quantity.
U.S. Pat. No. 2,917,110 discloses a filter in which the opening of the venting tube for fuel vapors is controlled by a bimetallic closing member. This filter can not be utilized for diesel fuel. The disadvantage of this filter is that the bimetallic valve member is exposed in the main flow on the clean side of the filter. Furthermore, the valve closing member is rather expensive, has a complex shape and carries out no snapping action. When the valve closing member closes the opening in the valve no continuous air venting takes place. In general there is no fuel return from the fuel injection pump in the known device.